Russell, in U.S. Pat. No. 2,898,356, disclosed that chelated titanium salts of .alpha.-hydroxy acids may be useful in the textile, leather and cosmetic industries, but that they may not be used at an alkaline pH. He proposed, therefore, a method for the preparation of a stabilized solution of such salts in alkaline aqueous media which comprises admixing a chelated titanium salt of an .alpha.-hydroxy acid with a polyol. He disclosed also that the chelated titanium salt of the .alpha.-hydroxy acid may be prepared by reacting an alkyl ester of ortho-titanic acid with an .alpha.-hydroxy acid or by reacting a titanium salt of an inorganic acid with an .alpha.-hydroxy acid. In the examples involving an inorganic titanium salt, Russell formed an aqueous solution of titanium tetrachloride or titanyl sulfate with sorbitol and then added malic or citric acid to it.
It has long been known that titanium esters react with high molecular weight hydroxyl-containing compounds so as to cross-link them and produce gels; J. Oil and Colour Chem. Assoc. 31, 405 (1948). However, the cross-linking reaction made through the use of simple alkyl esters of titanium proceeds too rapidly for most industrial uses. The cross-linking rate imparted by titanium esters can be depressed by combining a titanium ester with a variety of multi-functional compounds. For example, Shacklett, in U.S. Pat. No. 2,870,181, proposed a titanium compound prepared by reacting an orthotitanate with an .alpha.-hydroxy carboxylic acid in an organic solvent. It has also been proposed to combine a titanium ester with 2,4-pentanedione or with an acetoacetate; U.S. Pat. No. 2,680,108, The Organic Chemistry of Titanium by Feld et al., published by Butterworth (1965), and Yamamoto et al., JACS, 79 (1957), 4344-8. Alkanolamines, such as triethanolamine, have been used for that purpose as well; see U.S. Pat. Nos. 2,950,174 and 3,301,733.
For some time, it has been known also that the production of oil and gas can be stimulated by a technique, known as hydraulic fracturing, in which a fluid composition is introduced into an oil or gas well at a flow rate and pressure which create and/or extend a fracture into the oil- or gas-containing formation. The fluid composition usually carries a proppant (e.g., sand, bauxite, etc.) which is forced into the fracture by the fluid composition and prevents closure of the formation after the fluid pressure is released. For example, Crenshaw et al., in U.S. Pat. No. 3,634,237, disclosed fluid fracturing of oil and gas wells by the use of aqueous alcoholic solutions containing natural gums which had been thickened by the use of inorganic alkaline metal and alkaline earth metal salts. Likewise, Holtmyer et al., in U.S. Pat. No. 4,033,415, disclosed a fracturing fluid composed of a hydratable polysaccharide cross-linked in water by a cross-linking ion, e.g., Ti(IV) from TiCl.sub.4. In U.S. Pat. No. 3,888,312, Tiner et al. disclosed hydraulic fracturing of subterranean formations using an aqueous gel prepared from a solvatable polysaccharide which had been cross-linked with ammonium tetralactotitanate(IV) or bis(triethanolamine)bis(isopropyl)-titanium.
While a variety of modified titanium ester compositions is available commercially, there is a need to provide titanium based cross-linkers which are less expensive to prepare. Thus, the accepted method for manufacturing some of the modified titanates described above involves starting with a titanium ester, such as tetraisopropyltitanate. Most commonly, such esters are prepared by reacting TiCl.sub.4 with an appropriate alcohol in the presence of an amine and removing the by-product HCl as the amine salt. Thereafter the titanate is reacted with one of the modifying agents to give the titanium complex or chelate along with the by-product alcohol. It is common to use or sell the reaction product without removing the alcohol.
The process and the products of the present invention provide advantages over those of the prior art. The compositions of the present invention are more effective as cross-linkers than those of Russell. Moreover, the products of the present invention are prepared directly from the titanium salt, such as TiCl.sub.4, thus eliminating the step of preparing the titanate. In addition, the process and products of the present invention involve an aqueous medium, thereby avoiding flammability and pollution problems associated with some of the prior art methods.